1. Field of the Invention
The invention relates to a cooling and screening drum for tobacco materials comprising a material inlet, a rotary drum including lifting webs running longitudinally along the inner wall, a recirculating air system and a material outlet, wherein said lifting webs are configured inclined obliquely to said inner wall contrary to the direction of rotation of said drum.
2. Description of the Related Art
Tobacco materials, especially as employed in cigarette production, are dried in the course of their processing as cut tobacco. In prior art the dried cut tobacco is directed into a so-called cooling and sieve (screening) drum for it to be cooled and dedusted prior to further treatment, such as flavoring, for example, taking place.
Such cooling and screening drums are relatively large drum-shaped chambers having a material inlet and a material outlet rotating about their longitudinal axis thereby axially conveying the tobacco. The wall of the drum is configured like a strainer/sifter and the tobacco dust to be removed is drawn off downwards with the aid of an air flow acting transversely to the conveying direction. After having passed through the drum the tobacco is prepared for further treatment and may be flavored.
So that the tobacco may be adequately intermingled or tumbled in the drum, lifting or tumbling devices are provided on the inner wall of the drum which are variously configured in prior art. Thus, the KIM and KIMF type cooling and screening drums of the Korber Company comprise sheet metal webs radially extending from the drum inner wall towards the longitudinal axis featuring a relatively large radial height and running along the full length of the drum. In this case, for example, six such longitudinal plates are provided symmetrically distributed about the circumference in the drum.
The Swiss patent No. 229 145 shows a drum dryer having a perforated casing and transverse ventilation in which paddles having curved ends are provided running up to almost the drum axis as tumbling means.
Known from GB-A-502,225 is a rotary dryer for tobacco comprising blades protruding almost vertically at the inner circumference for distributing the tobacco. All of these known devices have in particular the disadvantage that the cut tobacco is subjected to very rough treatment on being introduced into the drum and during its conveyance. It receives heavy impact on impinging the radially arranged, relatively large tumbling means since on rotary movement of the drum it impacts the walls thereof mostly vertically. In addition to this, after slipping from the lifting edges it drops a long way to the bottom of the drum due to the relatively large, radial extent of the lifting edges.
The disadvantage resulting from such a rough treatment of the tobacco is that new tobacco dust materializes in the drum. In addition to this the filling capacity of the tobacco due to such treatment is reduced by up to 5%, i.e. an undesirable degradation of the tobacco occurs.